This invention relates to a control method for a multi-strand rolling mill, and more particularly to a method in which the control is responsive to at least one strand workpiece leaving or entering a roll stand, which roll stand is simultaneously rolling a plurality of strand workpieces, to remove the influence of the strand workpiece which has left or entered the stand on the remaining strand workpieces being rolled in the stand for a single roll stand and on the remaining strands being rolled in the roll stands for a multi-strand rolling mill.
Multi-strand rolling mills comprise a roll stand including a pair of upper and lower working rolls each having, for example, a pair of circumferentially extending grooves positioned in spaced relationship on the surface thereof and opposed to like grooves on the other working rolls. The grooves on the upper and lower working rolls form therebetween a roll opening the size of which is controllable by bilateral manual screw-down devices.
In operation, a pair of strand workpieces pass simultaneously through the roll opening between the working rolls so as to be simultaneously rolled into shapes determined by the shape of the opposed forming grooves. However, the trailing end of one of the strand workpieces may leave one of the spaces between the grooves in the upper and lower rolls before the other strand workpiece. This causes a change in roll opening. Also when a leading end of another strand workpiece enters the roll opening at the position of the empty opposite forming grooves, the roll opening is changed. Therefore the rolled strand may not be uniform in dimension due to this changing of the roll opening.
One example of multi-strand rolling mills comprises a plurality of roll stands disposed in tandem to roll simultaneously, for example, a pair of strand workpieces, and the plurality of roll stands is followed by a pair of branched arrays of roll stands disposed in tandem, one for each strand workpiece, so as to roll only one respective workpiece. Each of the roll stands for simultaneously rolling the pair of strand workpieces includes a pair of upper and lower working rolls as described above and each of the roll stands in the branched arrays includes a pair of upper and lower working rolls different from those described above only in that a single forming groove is provided in each working roll.
When the roll opening changes on one of the roll stands with the double grooved working rolls for the reason as described above, entry and delivery speeds of the strand workpieces in that roll stand change. As a result, the prior art multistrand rolling mill has been unable to keep a constant mass flow of the workpieces during the normal operation.
Although when at least one strand workpiece has left or entered an associated roll stand during the simultaneous rolling of a plurality of strand workpieces so that the entry and delivery speeds of the remaining strand workpieces change, conventional control methods for multi-strand rolling mills have not particularly compensated for the change in speed. Therefore each of the remaining strand workpieces being rolled on the roll stand has the loop disposed downstream thereof changed greatly with the result that all the roll stands downstream thereof are adversely affected. On the other hand, because that roll stand from which at least one strand workpiece has departed has a smaller mass flow therethrough than the roll stand upstream thereof, a compression force is generated on the remaining stand extending between those roll stands.
Accordingly it is an object of the present invention to provide a new control method for controlling a multi-strand rolling mill so that the roll opening is always maintained on any roll stand disposed in the rolling mill so as to roll simultaneously a plurality of strand workpieces regardless of whether or not only one of the strand workpieces is present in that roll stand.
It is another object of the present invention to provide a new control method controlling a multi-strand rolling mill comprising a plurality of roll stands disposed in tandem so that when at least one of a plurality of strand workpieces leaves or enters any one of the roll stands simultaneously rolling the strand workpieces, a constant mass flow of the strand workpieces is maintained throughout the rolling mills.